Castrol Cyltech Two-Stroke Cylinder Oils

Cyltech is Castrol's family of cylinder lubricants for the slow-speed, two-stroke crosshead engines that drive most large merchant ships; the oil is metered onto the liner and consumed with the charge rather than recirculated. What sets one grade apart from the next is its base number — the alkalinity reserve that counters the acids produced when sulphur-bearing fuel combusts. Castrol bands the Cyltech range by that figure so a chief engineer can pair the oil to whatever is in the bunkers: robust, high-BN grades for residual high-sulphur fuel oil, and leaner, lower-BN grades for the compliant low-sulphur fuels — VLSFO and LSFO — that have dominated since the 2020 cap. A mismatch bites either way: an oil too weak for the fuel lets acid pit and corrode the running surface, whereas an oil too strong for a clean fuel lays down surplus additive that glazes the bore. Engineers therefore tune cylinder condition through grade and feed rate together, reading drain-oil analysis to stay in balance. Each Cyltech grade catalogued here records its datasheet figures — BN, SAE grade, target fuels and OEM approvals — with the final pick to be set against the engine builder's approval and Castrol's advice for the specific engine and fuel.